The present invention relates to a method of lubrication between two sliding members at least one of which is made of a ceramic material and an apparatus for improving a lubrication between two sliding members at least one of which is made of a ceramic material.
Oils have conventionally been used in performing lubrication between two sliding members as in an automotive engine. A proposal has recently been made to use ceramic parts in the engine with a view to meeting various needs such as smaller cooling loss, lighter weight and better endurance under hostile operating conditions. Ceramic parts have such high heat resistance that they used not be cooled, thereby making it possible to reduce cooling loss.
On the other hand, ceramic parts become as hot as 300.degree. C. and higher if they are not cooled. Obviously, currently used oils are not suitable for lubricating such hot members. Solid lubricants could be used in place of oils but they have the disadvantage of high cost and maintenance of solid lubricant film.
For example, when bearings such as a ball-and-roller bearing and a slide (plain) bearing are to be used in a hot atmosphere, oils or greases cannot be used as lubricants. Under the circumstances, solid lubricants are conventionally used as a component of the bearing such as a retainer or coatings of solid lubricants are applied to the sliding part of that bearing component. However, these conventional bearings lubricated by the methods described above have had the following problems. First, in the case of using a solid lubricant as a bearing component, the latter may break during use since the solid lubricant is generally a low-strength and brittle material, thus reducing the strength of the bearing component. In the second case of applying a coating of solid lubricant, the coated solid film may spall off from the substrate, leading to deterioration in the lubricating characteristics of the film. As a further problem which is common to both cases, the solid lubricant cannot be replenished even if it is exhausted.